1. Field of the Invention
The present invention relates to an inkjet printer head equipped with a front head unit and an ink-channel defining unit which are connected to each other, and also an inkjet printer incorporating such an inkjet printer head.
2. Discussion of Related Art
There is known an inkjet printer arranged to perform a printing operation by ejecting ink droplets onto a print media (e.g., paper sheet) through nozzles in accordance with an input signal. Conventionally, such an inkjet printer includes a front head unit incorporating a member which is formed with nozzles, and the member formed with the nozzles provides an outside surface of the front head unit which surface is to be opposed to a print media. For example, U.S. Pat. No. 5,748,214 (corresponding to JP-A-H08-276586) discloses an inkjet printer head including a laminar-structured front head unit which is equipped with: a nozzle plate formed with a multiplicity of nozzles opening in its outside surface and arranged in a plurality of rows; a plurality of ink-channel defining plates defining ink channels; and a piezoelectric actuator capable of pressurizing an ink within each of the ink channels communicating with a corresponding one of the nozzles so that the ink is ejected through the corresponding nozzle. The inkjet printer head further includes an ink-channel defining unit (which is referred to as “head holder” in the U.S. Patent publication) which holds the front head unit and which supplies an ink into the front head unit through ink outlets and ink inlets respectively formed in the ink-channel defining unit and front head unit. The front head unit and the ink-channel defining unit are firmly fixed to each other through an adhesive which is applied onto mutually opposed surfaces thereof, with the ink outlets and inlets being mutually aligned.
Since the mutually aligned ink outlets and inlets open in the above-described mutually opposed surfaces (onto which the adhesive is applied), the adhesive could flow into the ink inlets, thereby possibly impeding supply of the ink from the ink-channel defining unit to the front head unit. The U.S. Patent Publication teaches a technique to prevent the adhesive from flowing into the above-described ink inlets. Specifically described, in the inkjet printer head disclosed in the U.S. Patent Publication, a protrusion is formed on the surface of the ink-channel defining unit so as to surround the openings of the ink outlets, so that the ink is inhibited by the protrusion, from flowing into the ink inlets (see FIG. 14 of the U.S. Patent Publication). The front head unit and the ink-channel defining unit are fixed to each other through the adhesive applied over wide areas of the mutually opposed surfaces except their portions in which the ink outlets and inlets open.
However, it is common that the front head unit and the ink-channel defining unit are made of a metallic material and a synthetic resin, respectively, which are considerably different from each other in coefficient of linear expansion. Therefore, the inkjet printer head is likely to suffer from an ink leakage due to separation of the front head unit and the ink-channel defining unit from each other, which separation could be caused as a result of its long-term service under an environment having temperature fluctuation.
It might be possible to reduce the areas at which the two units are bonded to each other, for preventing the separation of the two units. However, the reduction in the bonded areas leads to a reduction in rigidity of the front head unit, thereby possibly inducing a so-called “cross talk” between the adjacent rows of the nozzles. That is, pressure fluctuation occurred in each row of the nozzles could be propagated to another row of the nozzles, whereby a printing performance of the printer head is likely to be affected.
For preventing the separation of the two units, it might be also possible to interpose an elastic sealing member between the ink outlets of the ink-channel defining unit and the ink inlets of the front head unit. However, since the front head unit is thin as a whole in spite of its metallic laminar structure, the front head unit is likely to be warped or deformed by a reaction force exerted by the elastic sealing member which is compressed between the two units. If the front head unit is thus deformed, directions of the nozzles are problematically changed.
U.S. Pat. No. 6,652,081 (corresponding to JP-A-2003-145791) discloses an inkjet printer head equipped with a sealing system which enables the two units to be fixed to each other without warping or deforming the front head unit. The sealing mechanism includes a sleeve disposed on the ink inlet of the front head unit, an O-ring mounted on the sleeve, and a backup member disposed between the two units, such that the O-ring is pressed by the backup member against the ink-channel defining unit while at the same time being tightly fitted on an outer circumferential surface of the sleeve. In this sealing system, a reaction force exerted by the compressed O-ring acts on the backup member (which is held by a portion of the ink-channel defining unit) rather than on the front head unit (see FIGS. 10A and 10B of the U.S. Patent Publication). However, this sealing system requires the O-ring and the sleeve for the fluid-tight connection between the ink outlet and inlet, and also the backup member for the prevention of deformation of the front head unit, thereby leading to an increased number of required components and an increased number of required steps in its manufacturing process, and consequently resulting in a high cost of manufacture of the inkjet printer head. Further, since an adhesive is used for the disposition of sleeve on the ink inlet of the front head unit, this sealing system is likely to still suffer from the above-described conventionally experienced problem that the supply of the ink from the ink-channel defining unit to the front head unit could be impeded by the adhesive having flowed into the ink inlet.
On the other hand, there is also known an arrangement in which a driver circuit (for driving the front head unit) is mounted on a carriage that is reciprocatable in a primary scanning direction (i.e., direction perpendicular to a direction in which the print media is to be fed). In the inkjet printer having this arrangement, a printing operation is performed by ejecting the ink onto the print media through selected ones of the nozzles in response to a drive signal outputted from the driver circuit to the front head unit. In the printing operation, each time the signal is outputted from the driver circuit to the front head unit, a large amount of electric current momentarily flows through the driver circuit, thereby inducing an abrupt increase in temperature at the driver circuit. Since the number of the nozzles provided in the head unit has been increased for attending a need for printing a higher density of image at a higher speed, the driver circuit has to be equipped with an increased number of driver elements each serving exclusively for a corresponding one of the nozzles. That is, as a result of provision of the increased number of the nozzles, the number of the driver elements provided in the driver circuit has become larger, so that the temperature increase induced at the driver circuit has become more considerable. The considerable temperature increase caused deterioration and instability in electrical properties of the driver circuit, thereby impeding a stable ejection of the ink.
In view of this problem rising from the temperature increase, there has been designed an arrangement, as disclosed in JP-A-2003-237037, in which a heat conductive body is mounted on the carriage so that heat generated at the diver circuit can be dissipated. In the arrangement disclosed in JP-A-2003-237037, the heat conductive body is provided by a plate member which is bent to have a U shape in its cross section, and is fixed relative to the carriage, such that its central bottom portion is held in contact with the driver circuit which is mounted on the carriage, and such that major surfaces of its respective opposite end portions are held in substantially perpendicular to the primary scanning direction (in which the carriage is movable), whereby the generated heat can be effectively dissipated.
Further, there is also known an arrangement, as disclosed in JP-A-2000-103084, in which the ink is supplied to the front head unit mounted on the movable carriage, from an ink tank held stationary in a main body of the inkjet printer, via a flexible tube. However, in this arrangement, air inevitably permeates through the flexible tube and dissolving in the ink within the tube, because of properties of material forming the tube. The air or bubbles contained in the ink may cause failure in the ink ejection and the consequent deterioration in the quality of the printed image. It has been therefore necessary to provide a bubble collector or retainer chamber on an upstream side of the front head unit, for removing the bubbles from the ink.